From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To: stable@vger.kernel.org
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	patches@lists.linux.dev,
	Ben Horgan <ben.horgan@arm.com>,
	James Morse <james.morse@arm.com>,
	Catalin Marinas <catalin.marinas@arm.com>
Subject: [PATCH 7.0 1139/1146] arm_mpam: Improve check for whether or not NRDY is hardware managed
Date: Wed, 20 May 2026 18:23:09 +0200
Message-ID: <20260520162214.031540394@linuxfoundation.org>
In-Reply-To: <20260520162148.390695140@linuxfoundation.org>
References: <20260520162148.390695140@linuxfoundation.org>
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7.0-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Ben Horgan <ben.horgan@arm.com>

commit ccad6001be5c38426ccf45790c411467ad3c03c6 upstream.

mpam_ris_hw_probe_csu_nrdy() sets and clears MSMON_CSU.NRDY and checks
whether it's configuration sticks. However, hardware isn't given a chance
to disagree. Based on rule LRTGP, in MPAM specification IHI0099 version
B.b, the hardware will set NRDY if it needs time to establish a count after
a configuration change.

Enable the monitor so that NRDY becomes relevant and change the
configuration after clearing NRDY to try and coax the hardware into setting
it.

Fixes: 8c90dc68a5de ("arm_mpam: Probe the hardware features resctrl supports")
Cc: <stable@vger.kernel.org>
Signed-off-by: Ben Horgan <ben.horgan@arm.com>
Reviewed-by: James Morse <james.morse@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 drivers/resctrl/mpam_devices.c |   13 +++++++++++--
 1 file changed, 11 insertions(+), 2 deletions(-)

--- a/drivers/resctrl/mpam_devices.c
+++ b/drivers/resctrl/mpam_devices.c
@@ -634,8 +634,7 @@ static struct mpam_msc_ris *mpam_get_or_
  */
 static bool mpam_ris_hw_probe_csu_nrdy(struct mpam_msc_ris *ris)
 {
-	u32 now;
-	u32 mon_sel;
+	u32 now, mon_sel, ctl_val;
 	bool can_set, can_clear;
 	struct mpam_msc *msc = ris->vmsc->msc;
 
@@ -646,11 +645,21 @@ static bool mpam_ris_hw_probe_csu_nrdy(s
 		  FIELD_PREP(MSMON_CFG_MON_SEL_RIS, ris->ris_idx);
 	mpam_write_monsel_reg(msc, CFG_MON_SEL, mon_sel);
 
+	/* Hardware might ignore nrdy if it's not enabled */
+	ctl_val = MSMON_CFG_CSU_CTL_TYPE_CSU;
+	ctl_val |= MSMON_CFG_x_CTL_MATCH_PARTID;
+	ctl_val |= MSMON_CFG_x_CTL_MATCH_PMG;
+	ctl_val |= MSMON_CFG_x_CTL_EN;
+	mpam_write_monsel_reg(msc, CFG_CSU_FLT, 0);
+	mpam_write_monsel_reg(msc, CFG_CSU_CTL, ctl_val);
+
 	_mpam_write_monsel_reg(msc, MSMON_CSU, MSMON___NRDY);
 	now = _mpam_read_monsel_reg(msc, MSMON_CSU);
 	can_set = now & MSMON___NRDY;
 
 	_mpam_write_monsel_reg(msc, MSMON_CSU, 0);
+	/* Configuration change to try and coax hardware into setting nrdy */
+	mpam_write_monsel_reg(msc, CFG_CSU_FLT, 0x1);
 	now = _mpam_read_monsel_reg(msc, MSMON_CSU);
 	can_clear = !(now & MSMON___NRDY);
 	mpam_mon_sel_unlock(msc);